ESC vehicle driving dynamic control method based on rear wheel steering system

Abstract

The invention discloses an ESC vehicle driving dynamic control method based on a rear wheel steering system, and belongs to the field of vehicle dynamic control, and the method comprises the following steps: S1, determining the steering transmission ratio of a vehicle; s2, determining generalized characteristic vehicle speeds of the vehicle under various working conditions; s3, a rear wheel steering angle is imported to determine the yaw velocity of a reference vehicle; s4, whether the ESC system is activated or not is determined based on the difference value between the reference vehicle yaw velocity and the actual vehicle yaw velocity, and when the ESC system is activated, the step S5 is executed; and S5, calculating a control quantity by taking the difference value as a return quantity of closed-loop control. By the adoption of the ESC vehicle running dynamic control method based on the rear wheel steering system, the rear wheel steering angle is introduced into the two-degree-of-freedom model, the calculation accuracy of the ESC reference yaw velocity is improved, and the problem that due to the fact that the two-degree-of-freedom model does not consider the influence of the rear wheel yaw angle on the vehicle dynamic characteristics, ESC misoperation or no operation is caused is solved.

Description

Technical Field

[0001] The invention relates to the technical field of vehicle dynamic control, and in particular to an ESC vehicle driving dynamic control method based on a rear wheel steering system. Background Art

[0002] The traditional ESC (electronic stability control system) calculates the reference vehicle yaw rate ω based on the two-degree-of-freedom vehicle model and the steering wheel angle input by the driver. ref (Refer to yaw rate). At the same time, the system measures the actual vehicle yaw rate ω through the inertial sensor IMU act (actual yaw rate) to determine the current stability of the vehicle and control it accordingly.

[0003] However, the traditional two-degree-of-freedom vehicle model only considers the front wheel swing angle as input. Therefore, for traditional vehicles that only use the front-wheel steering system, this model can more accurately calculate the reference vehicle yaw rate. For vehicles equipped with a rear-wheel steering system, when the driver steers through the steering wheel, the front wheels and the steering wheel are mechanically connected, and the front wheel swing angle is determined by the driver's steering wheel input. The rear-wheel steering system changes the rear wheel swing angle by driving the rear steering rod through the drive motor according to its own control logic (the rear wheel swing angle is determined by the software and control strategy of the rear-wheel steering).

[0004] It can be seen that since the traditional two-degree-of-freedom vehicle model only introduces the front wheel swing angle for calculation, it is unable to identify the impact of the rear wheel swing angle on the vehicle's yaw rate. Therefore, when the front and rear wheels have swing angles at the same time, the reference vehicle yaw rate calculated by the ESC system based on the traditional two-degree-of-freedom model will be distorted and cannot accurately reflect the vehicle's true stability state. This distortion will cause the ESC system to over-control or under-control under certain working conditions, thereby reducing the vehicle's handling stability.

[0005] At the same time, in the traditional vehicle dynamics definition, the vehicle speed at which the yaw rate gain reaches the maximum value in the vehicle steady-state response is called the characteristic vehicle speed V char , to express the understeering characteristics of the vehicle, which is determined by the vehicle's steering geometry and chassis design. It can be seen that for non-rear-wheel steering vehicles, the characteristic speed is a unique value, and the unique characteristic speed V char The yaw rate gain characteristics of a rear-wheel steering vehicle cannot be adequately described. Summary of the invention

[0006] The purpose of the present invention is to provide an ESC vehicle driving dynamics control method based on a rear-wheel steering system to solve the above technical problems.

[0007] To achieve the above object, the present invention provides an ESC vehicle driving dynamics control method based on a rear-wheel steering system, comprising the following steps:

[0008] S1, determining the steering gear ratio of the vehicle, and storing the steering gear ratio in the ESC system for reference when the vehicle is running;

[0009] S2, determining the generalized characteristic speed of the vehicle under various operating conditions, and inputting the generalized characteristic speed into a three-dimensional map for table lookup when the vehicle is running;

[0010] S3, based on the output results of step S1 and step S2, importing the rear wheel steering angle to determine the reference vehicle yaw rate;

[0011] S4, determining whether the ESC system is activated based on the difference between the reference vehicle yaw rate obtained in step S3 and the actual vehicle yaw rate, and when the ESC system is activated, executing step S5;

[0012] S5. Taking the difference between the reference vehicle yaw rate and the actual vehicle yaw rate as the return amount of the closed-loop control, calculate the control amount, and perform control based on the control amount.

[0013] Preferably, in step S1, the front wheels of the vehicle are parked on a horizontally rotating angle measuring instrument, the driver turns the steering wheel from the left maximum steering angle to the right maximum angle, and reads the steering wheel angle signal SAR through the CAN bus, and at the same time reads the front wheel swing angle δ through the angle measuring instrument front , and calculate the vehicle's steering gear ratio SGR by the following formula:

[0014] SGR=SAR×δ front .

[0015] Preferably, in step S2, the vehicle is started, the ESC system software control function is turned off, and the rear-wheel steering system is turned on. The driver drives in a steady state around a circular road with a fixed radius at various speeds, and measures and records the generalized characteristic vehicle speed Vchar under various working conditions. gen , get the generalized characteristic speed Vchar gen , vehicle speed V ref and lateral acceleration Lat Acc The relationship between the generalized characteristic vehicle speed Vchar gen , vehicle speed V ref and lateral acceleration Lat Acc Input the 3D spectrum map for reference when the vehicle is running.

[0016] Preferably, in step S3, the vehicle is started, the ESC system software control function and the rear-wheel steering system are turned on, and the driver drives the vehicle normally. The ESC system calculates the reference vehicle yaw rate ω using the following expression: ref :

[0017]

[0018] In the formula, δ rear Indicates the rear wheel swing angle;

[0019] Among them, the steering gear ratio SGR and the generalized characteristic vehicle speed Vchar gen All obtained by looking up the table.

[0020] Preferably, in step S4, when the reference vehicle yaw angular velocity ω ref The actual vehicle yaw rate ω measured by the inertial sensor IMU act When the difference Δω between them exceeds a preset threshold, the ESC system is activated and step S5 is executed; otherwise, the vehicle keeps running normally.

[0021] Preferably, in step S5, the control amount u is calculated as follows:

[0022] u=u P +u I +u D

[0023] In the formula, u P represents the proportional term, and u P =K P ×Δω,K P represents the proportional gain, Δω represents the error; u I represents the integral term, and u I =K I ×∫Δω,dt,K I Indicates the integral gain; u D represents the differential term, and K D represents the differential gain;

[0024] When Δω is greater than the positive threshold, the ESC system determines that the vehicle is oversteering at this time, and the vehicle yaw rate ω read by the IMU is compared with the current steering wheel angle of the vehicle. act and lateral acceleration Lat Acc p determines the current vehicle steering direction and converts u into the brake hydraulic pressure request BrakePressureRequest_OuterFront of the outer front wheel according to the conversion coefficient KTorqueToPressure:

[0025] BrakePressureRequest_OuterFront=KTorqueToPressure×u

[0026] The ESC system's own pressure control module brakes the outer front wheel to reduce the actual vehicle yaw rate ω act , which in turn reduces oversteering and restores vehicle stability;

[0027] When Δω is less than the negative threshold, the ESC system determines that the vehicle is understeering and brakes the inner wheels of the vehicle through the actuator to increase the actual vehicle yaw angular velocity ω. act , which in turn reduces understeer and restores vehicle stability.

[0028] Therefore, the present invention adopts the above-mentioned ESC vehicle driving dynamic control method based on the rear-wheel steering system, which has the following beneficial effects:

[0029] 1. Improve vehicle stability: By accurately calculating and controlling the vehicle's yaw rate, the vehicle can be ensured to remain stable under complex driving conditions such as high-speed turns and emergency obstacle avoidance.

[0030] The addition of rear-wheel steering (ACK) further enhances the vehicle's handling, especially at low and high speeds.

[0031] 2. Optimize steering response: Through the precise calculation of the steering gear ratio (SGR) and the generalized characteristic vehicle speed (Vchar_gen), the vehicle's response at different speeds and steering angles is ensured to be more sensitive and accurate;

[0032] 3. Improve driving safety: When the ESC system detects that the deviation between the vehicle's yaw rate and the target value exceeds the threshold, it can intervene and adjust the vehicle status in time to avoid loss of control or skidding;

[0033] Real-time monitoring and closed-loop control mechanisms improve vehicle safety performance;

[0034] 4. The addition of the rear-wheel steering system (ACK) not only improves the vehicle's handling performance, but also provides additional stability support in emergency situations. For example, at low speeds, the rear wheels turn in opposite directions to reduce the turning radius and improve flexibility; at high speeds, the rear wheels turn in the same direction to improve stability in straight-line driving;

[0035] 5. Improve driving experience: Through precise control and optimized steering response, the driver can experience a smoother and safer driving experience during driving, reducing driving fatigue and risks caused by vehicle instability.

[0036] In summary, by comprehensively considering the vehicle's front wheel steering, rear wheel steering and real-time yaw rate control, the vehicle's stability and safety under various driving conditions are significantly improved. This is of great significance for improving driving experience and reducing traffic accidents.

[0037] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A flow chart of the ESC vehicle driving dynamics control method based on the rear-wheel steering system of the present invention;

[0039] Figure 2 A two-dimensional representation of the ESC vehicle driving dynamics control method based on the rear-wheel steering system of the present invention;

[0040] Figure 3 A schematic diagram of a three-dimensional map spectrum of an ESC vehicle driving dynamics control method based on a rear-wheel steering system according to the present invention;

[0041] Figure 4 This is a comparison chart of the yaw rate of the reference vehicle calculated by the traditional method and the actual vehicle yaw rate in the actual vehicle verification example;

[0042] Figure 5 This is a comparison chart of the yaw rate of a reference vehicle calculated using the method of the present invention and the yaw rate of an actual vehicle in a real vehicle verification example. DETAILED DESCRIPTION

[0043] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the invented product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description of the present invention, it should also be noted that, unless otherwise clearly specified and limited, the terms "setting", "installation", and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0044] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0045] like Figure 1As shown, a driving dynamics control method of an ESC vehicle based on a rear-wheel steering system comprises the following steps:

[0046] S1, determining the steering gear ratio of the vehicle, and storing the steering gear ratio in the ESC system for reference when the vehicle is running;

[0047] In step S1, the front wheels of the vehicle are parked on a horizontally rotating angle measuring instrument. The driver turns the steering wheel from the maximum left steering angle to the maximum right angle, and reads the steering wheel angle signal SAR through the CAN bus. At the same time, the front wheel swing angle δ is read through the angle measuring instrument. front , and calculate the vehicle's steering gear ratio SGR by the following formula:

[0048] SGR=SAR×δ front .

[0049] S2, determining the generalized characteristic speed of the vehicle under various operating conditions, and inputting the generalized characteristic speed into a three-dimensional map for table lookup when the vehicle is running;

[0050] In step S2, the vehicle is started, the ESC system software control function is turned off, and the rear-wheel steering system is turned on. The driver drives in a steady state around a circular road with a fixed radius at various speeds, and measures and records the generalized characteristic vehicle speed Vchar under various working conditions. gen , get the generalized characteristic speed Vchar gen , vehicle speed V ref and lateral acceleration Lat Acc The relationship between the generalized characteristic vehicle speed Vchar gen , vehicle speed V ref and lateral acceleration Lat Acc Input the 3D spectrum map for reference when the vehicle is running.

[0051] S3, based on the output results of step S1 and step S2, importing the rear wheel steering angle to determine the reference vehicle yaw rate;

[0052] In step S3, the vehicle is started, the ESC system software control function and the rear-wheel steering system are turned on, and the driver drives the vehicle normally. The ESC system calculates the reference vehicle yaw rate ω using the following expression: ref :

[0053]

[0054] In the formula, δ rear represents the rear wheel swing angle; among them, the steering gear ratio SGR and the generalized characteristic vehicle speed Vchar gen All are obtained by looking up the table, such as Figure 2As shown, in this embodiment, SGR is obtained by looking up a two-dimensional table with SAS as input; Figure 3 As shown, Vchar gen By checking V ref and Lat Acc It is obtained by inputting the three-dimensional spectrum table.

[0055] S4, determining whether the ESC system is activated based on the difference between the reference vehicle yaw rate obtained in step S3 and the actual vehicle yaw rate, and when the ESC system is activated, executing step S5;

[0056] In step S4, when the reference vehicle yaw rate ω ref The actual vehicle yaw rate ω measured by the inertial sensor IMU act When the difference Δω between them exceeds a preset threshold, the ESC system is activated and step S5 is executed; otherwise, the vehicle keeps running normally.

[0057] S5. Taking the difference between the reference vehicle yaw rate and the actual vehicle yaw rate as the return amount of the closed-loop control, calculate the control amount, and perform control based on the control amount.

[0058] In step S5, the control amount u is calculated as follows:

[0059] u=u P +u I +u D

[0060] In the formula, u P represents the proportional term, and u P =K P ×Δω,K P represents the proportional gain, Δω represents the error; u I represents the integral term, and u I =K I ×∫Δω,dt,K I Indicates the integral gain; u D represents the differential term, and K D represents the differential gain;

[0061] When Δω is greater than the positive threshold, the ESC system determines that the vehicle is oversteering at this time, and the vehicle yaw rate ω read by the IMU is compared with the current steering wheel angle of the vehicle. act and lateral acceleration Lat Acc p determines the current vehicle steering direction and converts u into the brake hydraulic pressure request BrakePressureRequest_OuterFront of the outer front wheel according to the conversion coefficient KTorqueToPressure:

[0062] BrakePressureRequest_OuterFront=KTorqueToPressure×u

[0063] The ESC system's own pressure control module brakes the outer front wheel to reduce the actual vehicle yaw rate ω act , which in turn reduces oversteering and restores vehicle stability;

[0064] When Δω is less than the negative threshold, the ESC system determines that the vehicle is understeering and brakes the inner wheels of the vehicle through the actuator to increase the actual vehicle yaw angular velocity ω. act , which in turn reduces understeer and restores vehicle stability.

[0065] Real vehicle verification example

[0066] In a vehicle ESC system equipped with a rear-wheel steering system, the conventional reference vehicle yaw rate ωref is first calculated using the conventional method. old Then, the software of the present invention is flashed again in the ESC system of the same vehicle to calculate the reference vehicle yaw rate ωref. new The software is used to conduct sinusoidal steering input experiments.

[0067] The result is as follows Figure 4 and Figure 5 As shown, it can be seen that when the traditional method is used, the calculated reference vehicle yaw angular velocity ωref old and the actual vehicle yaw rate ω act The large difference causes the ESC system to control the vehicle yaw too early and too strongly, which causes the vehicle to yaw in a manner that does not meet the driver's expectations and reduces the vehicle's handling stability. new and the actual vehicle yaw rate ω act The difference is small and is within the threshold of the ESC system stability control activation. The ESC system will not be activated prematurely, the control level is appropriate, and the vehicle handling stability performance is improved, thereby verifying the effectiveness of the present invention.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A driving dynamics control method of an ESC vehicle based on a rear-wheel steering system, characterized in that: The following steps are involved: S1, determining the steering gear ratio of the vehicle, and storing the steering gear ratio in the ESC system for reference when the vehicle is running; S2, determining the generalized characteristic speed of the vehicle under various operating conditions, and inputting the generalized characteristic speed into a three-dimensional map for table lookup when the vehicle is running; S3, based on the output results of step S1 and step S2, importing the rear wheel steering angle to determine the reference vehicle yaw rate; S4, determining whether the ESC system is activated based on the difference between the reference vehicle yaw rate obtained in step S3 and the actual vehicle yaw rate, and when the ESC system is activated, executing step S5; S5. Taking the difference between the reference vehicle yaw rate and the actual vehicle yaw rate as the return amount of the closed-loop control, calculate the control amount, and perform control based on the control amount.

2. The ESC vehicle driving dynamics control method based on the rear-wheel steering system according to claim 1, characterized in that: In step S1, the front wheels of the vehicle are parked on a horizontally rotating angle measuring instrument. The driver turns the steering wheel from the maximum left steering angle to the maximum right angle, and reads the steering wheel angle signal SAR through the CAN bus. At the same time, the front wheel swing angle δ is read through the angle measuring instrument. front , and calculate the vehicle's steering gear ratio SGR by the following formula: SGR=SAR×δ front 。 3. The ESC vehicle driving dynamics control method based on the rear-wheel steering system according to claim 2 is characterized in that: In step S2, the vehicle is started, the ESC system software control function is turned off, and the rear-wheel steering system is turned on. The driver drives in a steady state around a circular road with a fixed radius at various speeds, and measures and records the generalized characteristic vehicle speed Vchar under various working conditions. gen , get the generalized characteristic speed Vchar gen , vehicle speed V ref and lateral acceleration Lat Acc The relationship between the generalized characteristic speed Vchar gen , vehicle speed V ref and lateral acceleration Lat Acc Input the 3D spectrum map for reference when the vehicle is running.

4. The ESC vehicle driving dynamics control method based on the rear-wheel steering system according to claim 3 is characterized in that: In step S3, the vehicle is started, the ESC system software control function and the rear-wheel steering system are turned on, and the driver drives the vehicle normally. The ESC system calculates the reference vehicle yaw rate ω using the following expression: ref : In the formula, δ rear Indicates the rear wheel swing angle; Among them, the steering gear ratio SGR and the generalized characteristic vehicle speed Vchar gen All obtained by looking up the table.

5. The ESC vehicle driving dynamics control method based on the rear-wheel steering system according to claim 4 is characterized in that: In step S4, when the reference vehicle yaw rate ω ref The actual vehicle yaw rate ω measured by the inertial sensor IMU act When the difference Δω between them exceeds a preset threshold, the ESC system is activated and step S5 is executed; otherwise, the vehicle keeps running normally.

6. The ESC vehicle driving dynamics control method based on the rear-wheel steering system according to claim 5, characterized in that: In step S5, the control amount u is calculated as follows: in=in P +in I +in D In the formula, u P represents the proportional term, and u P =K P ×Δω,K P represents the proportional gain, Δω represents the error; u I represents the integral term, and u I =K I ×∫Δω,dt,K I Indicates the integral gain; u D represents the differential term, and K D represents the differential gain; When Δω is greater than the positive threshold, the ESC system determines that the vehicle is oversteering at this time, and the vehicle yaw rate ω read by the IMU is compared with the current steering wheel angle of the vehicle. act and lateral acceleration Lat Acc p determines the current vehicle steering direction and converts u into the brake hydraulic pressure request BrakePressureRequest_OuterFront of the outer front wheel according to the conversion coefficient KTorqueToPressure: BrakePressureRequest_OuterFront=KTorqueToPressure×u The ESC system's own pressure control module brakes the outer front wheel to reduce the actual vehicle yaw rate ω act , which in turn reduces oversteering and restores vehicle stability; When Δω is less than the negative threshold, the ESC system determines that the vehicle is understeering and brakes the inner wheels of the vehicle through the actuator to increase the actual vehicle yaw angular velocity ω. act , which in turn reduces understeer and restores vehicle stability.

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